Coupling



FIG. 1 is a front view of a coupling;

FIG. 2 is a top view, thereof;

FIG. 3 is a bottom view, thereof;

FIG. 4 is a top perspective view, thereof; and,

FIG. 5 is a bottom perspective view, thereof.

The broken lines are included for the purpose of illustrating portions of the coupling and forms no part of the claimed design. 

I claim the ornamental design for a coupling, as shown and described. 